Production plant of metal rods, casting machine, casting process and control method of electromagnetic stirrer devices of molten metal

ABSTRACT

Production plant of metal rods, casting machine, casting process and control method of at least three electromagnetic stirrer devices, wherein one provides at least one phase of switching between two operating configurations of the electromagnetic stirrer devices of which a first operating configuration with the generation of a rotating electromagnetic field inducing in the metallic material in the molten state a rotational motion and a second operating configuration with the generation of a linear electromagnetic field inducing in the metallic material in the molten state a linear motion.

TECHNICAL FIELD

The present invention relates to a control method of electromagneticstirrer devices of metallic material in the molten state in a castingmachine according to the characteristics of the pre-characterizing partof claim 1.

The present invention also relates to a casting machine according to thecharacteristics of the pre-characterizing part of claim 8.

The present invention also relates to a production plant of metallicmaterial rods according to the characteristics of the pre-characterizingpart of claim 12.

The present invention also relates to a casting process for theproduction of metallic material rods according to the characteristics ofthe pre-characterizing part of claim 13.

Definitions

In the present description and in the appended claims the followingterms must be understood according to the definitions given in thefollowing.

By the expression “metal rod” one means all kinds of products of acasting machine, such as billets, blooms or slabs with different shapesin section such as with a square, rectangular, round, polygonal section.

By the expression “casting machine” one means both vertical castingmachines and bending-type casting machines.

Prior Art

In the field of the production of steel or, in general, of metals andmetal alloys, an essential role is played by continuous castingmachines. Casting is a production process which allows to producesteelwork semi-finished products called billets, blooms, slabs dependingon their size and shape. The production of the semi-finished productsoccurs starting from the metal or metal alloy in the molten state whichis cast in a mould cooled by means of a cooling fluid which flowsaccording to a direction in counter-current with respect to thedirection of advancement of the metallic semi-finished product which isprogressively formed within the volume of the mould. The mould is placedaccording to an essentially vertical arrangement. The mould is open atits lower end from which the semi-finished product being formed comesout. The mould is open at its upper end from which the liquid metalenters, which progressively begins to solidify within the mould to bethen extracted from the lower end of the mould. The process isstationary, meaning that in the unit of time an amount of metal at leastpartially solidified comes out from the lower part of the mould, whichcorresponds to the amount of liquid metal which enters the mould on itsupper part. Once the casting process has been started, the level of theliquid metal within the mould is kept essentially constant, that is tosay, the position of the free surface of the liquid metal, that is tosay, the position of the so-called meniscus, with respect to theinternal wall of the mould is kept essentially constant in time duringthe process. In order to keep the level of the liquid metal constant,that is to say, to keep the position of the meniscus constant, it ispossible to act by varying the speed of extraction of the material beingformed in the mould or it is possible to act by varying the flow ofliquid metal which enters the mould from its upper end. This occurs onthe basis of the detection of the position of the meniscus in the mould.

In the field of the production of continuous casting plants of metallicmaterials, in general steels and metal alloys, it is also known toresort to electromagnetic stirring devices of the metallic material inthe molten state, generally known as stirrers. The stirrer produces anelectromagnetic field generating a force inside the die or mould withinwhich the metallic material in the molten state is inducing a movementflow inside the molten bath obtaining a stirring effect of the latter.In the die or mould the cooling of the surface or skin of the metal rodwhich is generated in the die occurs and, in correspondence of the exitof the metal rod from the die or mould, it has a solidified perimeterzone or shell having a thickness of 10-30 mm inside which there is acore in which the metallic material is still in the molten state andwhich is progressively solidified upon advancement of the metal rodwithin a cooling chamber of the casting machine in which it is subjectedto the action of cooling units, which generally consist of a series ofwater sprayers. Applications of the stirrers are known both incorrespondence of the die or mould within which the introduction of themetallic material in the molten state occurs and applications of thestirrers in correspondence of the cooling chamber of the casting machineto obtain improvements in the quality of the structure of the metal rodand reduce the occurrence of defects.

The stirrer consists of a casing inside which electrical windings arearranged for the passage of a current which induces an electromagneticstirring field. The casing has an open duct within which the hot rodpasses. For example the use of stirrers contributes to reducingsuperficial and under-skin blowholes and inclusions, cracks, porosity,segregation and contributes to improving the solidification structures.

Two essential types of stirrers are known, which are the stirrers of therotary type and the stirrers of the linear type. In the case of thestirrers of the rotary type, the stirrer produces an electromagneticfield generating a force inside the die or mould within which themetallic material in the molten state is inducing a rotating flow insidethe molten bath in which the rotating flow occurs on a plane which isessentially orthogonal to the direction of extraction of the metal rodbeing formed in the mould, obtaining the stirring effect of the moltenbath itself. In the case of the stirrers of the linear type, the stirrerproduces an electromagnetic field generating a force inside the die ormould within which the metallic material in the molten state is inducinga flow inside the molten bath in which the flow is oriented according toa direction which is essentially parallel with respect to the directionof extraction of the metal rod being formed in the mould, obtaining thestirring effect of the molten bath itself.

Continuous casting machines and semi-continuous casting machines areknown, such as those described in WO 2015 079071 which describes amethod for the semi-continuous casting of a strand of steel, in which acontrolled cooling of the semi-solidified strand is provided after itsextraction from the mould until complete solidification of the strand,the cooling occurring in a tertiary cooling zone of the casting machine.

Solutions of stirrers which are mobile along different positions in thecasting chamber of a casting machine are known, such as the solutiondescribed in WO 2013/174512 in the name of the same applicant, to beconsidered as incorporated for reference.

Patent application CN 103 182 495 describes a multifunctionalelectromagnetic stirrer, comprising six layers of annular cores whichare horizontally arranged, six rack cores which are vertically arrangedand thirty-six identical solenoid coil windings. The six layers ofannular cores are mutually independent layer by layer. The six layers ofannular cores are aligned vertically and are separated at intervals. Theinner wall of each layer of annular core is provided with six salientpoles. The six rack cores are uniformly distributed on the outer wallsof the annular cores; each rack core is provided with five salientpoles. The salient poles of the rack cores are inserted into theintervals, which are vertically separated, of the annular poles. Thesalient poles of each rack core and the salient poles of the six layersof annular cores are located on the same circumference. The top surfacesof the salient poles of each rack core are inserted into the inner wallsbetween the salient poles of the annular cores. The thirty-six solenoidcoil windings are respectively sleeved on each salient pole of theannular cores. A three-phase low-frequency alternating current issupplied by a variable-frequency power source. According to thedisclosed solution the described structure can be used as a structuralbase for configuring different modes of connection of the coilsinstalled in correspondence of the different poles in such a way thatthe base structure can be made independently of the followingconfiguration of connection of the coils and, therefore, subsequentlypersonalized and configured in a fixed way according to the desiredconnection diagram of the coils.

Patent application EP 0 080 326 describes a casting machine comprising amould and electromagnetic stirring means located about the metal strandpath. The electromagnetic stirring means comprise a set ofelectromagnetic coils disposed about the strand. The set of coils isconnected to two separate power sources by means of two separate sets ofconnections such that one power supply and set of connections activatesthe set of coils to provide a rotational field force upon the strand,and the other power supply and set of connections activates the set ofcoils to provide an axial field force upon the strand.

Problems of the Prior Art

The prior art solutions are generally limited to the alternativeapplication of one type of stirrers or of the other, that is to say,there exist casting machines provided with rotary stirrers and castingmachines provided with linear stirrers.

The combination of the two operating modes is not contemplated due tothe incompatibility of the devices used in the two configurations. Thatis to say, if a casting machine is configured with inverters andstirrers, which are suitable for operation as rotary stirrers, it isunsuitable for operation as a casting machine with linear stirrers. Viceversa, if a casting machine is configured with inverters and stirrerssuitable for operation as linear stirrers, it is unsuitable foroperation as a casting machine with rotary stirrers.

Aim of the Invention

The aim of the present invention is to provide a stirrer and a controlmethod of the stirrer which allows for a configurability between anoperating condition in which the stirrer acts as a rotary stirrer and anoperating condition in which the stirrer acts as a linear stirrer.

Concept of the Invention

The aim is achieved by the characteristics of the main claim. Thesub-claims represent advantageous solutions.

Advantageous Effects of the Invention

The solution according to the present invention, by the considerablecreative contribution the effect of which constitutes an immediate andimportant technical progress, presents various advantages.

The configurability of the stirrer between the operating modes as arotary stirrer and a linear stirrer on a same casting machine allows tobe able to operate with a same casting machine according to differentoperating modes which are respectively suitable for the casting ofdifferent types of cast product with different qualities, which,according to the available prior art solutions, would require, on theother hand, the use of two different casting machines. Advantageously,the described solution allows to realize casting machines which areeasily configurable between different operating conditions, such as afirst operating configuration in which one single product is cast in thecasting machine, which may be subjected to a stirring action of themolten bath by means of a rotary or linear stirrer or a combinationthereof with alternate phases of rotary stirring and of linear stirring,and a second operating configuration in which two products aresimultaneously cast in the casting machine on parallel casting lines ofthe same machine, wherein each of the two cast products is subjected toa stirring action of the molten bath by means of stirrers exploiting thesame devices used to obtain the stirring of the molten bath in the firstoperating configuration. Particularly in the first operatingconfiguration, the solution according to the present invention thusallows to be able to benefit from both methods of rotary stirrer andlinear stirrer combining their benefits and consequently improving thefinal results. Particularly in the second operating configuration, thesolution according to the present invention also allows to be able touse the same casting machine according to operating modes with a highproductivity of metal rods, enabling the production of multiple metalrods on the same casting machine.

DESCRIPTION OF THE DRAWINGS

In the following a solution is described with reference to the encloseddrawings, which are to be considered as a non-exhaustive example of thepresent invention in which:

FIG. 1 shows a casting machine incorporating the system according to theinvention.

FIG. 2 shows a three-phase inverter for the driving of a stirrer.

FIG. 3 shows a three-phase inverter suitable for the driving of a linearstirrer.

FIG. 4 shows the power stage of a three-phase inverter for the drivingof a linear stirrer.

FIG. 5 and FIG. 6 schematically show the trends of the voltage andcurrent waveforms in the case of a connection configuration as in FIG.4.

FIG. 7 shows a diagram of an inverter suitable for the driving of alinear stirrer.

FIG. 8 represents a connection single line diagram in the case of aparticular application of the present invention.

FIG. 9 represents a schematic view of a first operating configuration ofa casting machine in which one single product is cast.

FIG. 10 shows a schematic view of a second operating configuration ofthe casting machine of FIG. 9 in which two products are simultaneouslycast on parallel casting lines of the same machine.

FIG. 11 shows a schematic view of the effect of linear stirrers on oneof the casting lines in the case of a first control mode of the linearstirrers.

FIG. 12 shows a schematic view of the effect of linear stirrers on oneof the casting lines in the case of a second control mode of the linearstirrers.

FIG. 13 and FIG. 14 schematically show an application of the presentinvention with a mobile stirrer in a bending-type casting machine.

FIG. 15 schematically shows an application of the present invention witha mobile stirrer in a vertical casting machine.

DESCRIPTION OF THE INVENTION

With reference to the figures (FIG. 1, FIG. 9, FIG. 10, FIG. 11, FIG.12) the present invention relates to an electromagnetic stirrer device(1, 1′, 1″, 1′″, 1″″) of metallic material in the molten state of thetype usually called “stirrer”. The electromagnetic stirrer device (1)according to the present invention is intended to be applied in acasting machine (18). The system according to the invention is suitablefor the application both on casting machines (18) of the continuous typeand on casting machines of the semi-continuous type. An example ofcasting machines of the semi-continuous type is given by the solutiondescribed in WO 2015 079071, which is to be considered as incorporatedfor reference, which describes a method for the semi-continuous castingof a strand of steel, in which a controlled cooling of thesemi-solidified strand is provided after its extraction from the moulduntil complete solidification of the strand, the cooling occurring in atertiary cooling zone of the casting machine.

In general the solution according to the invention is suitable both forcasting machines of the vertical type (FIG. 15) and for bending-typecasting machines (FIG. 13, FIG. 14). In general (FIG. 1) in the castingmachine (18) the metallic material in the molten state is cast from atundish (19) into a mould (14) placed below the tundish (19) and inwhich the metallic material rod (16) comes out of the mould on its lowerpart according to a direction of extraction (22). The metallic materialrod (16) may be, by way of example and without limitation for thepurposes of the present invention, a billet, a bloom or a slab withdifferent shapes in section, such as with a square, rectangular, round,polygonal section. In the present description and in the appended claimsby the expression “casting machine” one thus means vertical castingmachines, bending-type casting machines, continuous casting machines,semi-continuous casting machines. The electromagnetic stirrer device (1,1′, 1″, 1′″, 1″″) exerts a stirring force by means of the application ofa current of generation of an electromagnetic field through windings orinduction coils (20′, 20″, 20′″). The stirring force acts incorrespondence of the partially solidified metallic material rod (16)being formed within the mould (14) but one may also provide embodimentsin which the stirring action is induced on the partially solidifiedmetallic material rod (16) after it has already come out of the mould(14). In fact, when the metallic material rod (16) comes out of themould (14) it is not in a condition of complete solidification yet butthe metallic material rod (16) consists of a shell in the solid stateenclosing a core in the molten state. In this case, the electromagneticstirring device (1, 1′, 1″, 1′″, 1″″) acts and exerts its own action bymeans of the electromagnetic stirring field on the core in the moltenstate of the partially solidified metallic material rod (16). In thecase of the application in the mould the field acts on the metallicmaterial in the molten state, which is kept at a constant levelbalancing the amount of material introduced into the mould and materialextracted from the mould in such a way that the meniscus (15) isapproximately always in the same position inside the mould.

The electromagnetic stirrer device (1, 1′, 1″, 1′″, 1″″, 11 a, 11 b) isdriven (FIG. 2, FIG. 3, FIG. 4, FIG. 7, FIG. 8) by means of inverters(2, 2′, 2″, 2′″, 2″″). The inverters are devices suitable to convert amains three-phase alternating voltage, having fixed voltage andfrequency, provided at a power supply input (3), into a drivingalternating voltage of variable amplitude and having a frequency whichis set on the basis of a reference signal provided at a reference input(4) of the inverter (2, 2′, 2″, 2′″, 2″). The inverters are deviceswhich are further suitable to convert a voltage provided at a powersupply input (3) as input direct current into a driving alternatingvoltage of variable amplitude and having a frequency which is set on thebasis of a reference signal provided at a reference input (4) of theinverter (2, 2′, 2″, 2′″, 2″″). According to the inverter model it ispossible to connect at the output a load to be driven which can be abalanced load with 2 or 3 phases or an unbalanced load with 3 phases, asin the case of a stirrer or electromagnetic stirrer device (1,1′, 1″,1′″, 1″″, 11 a, 11 b).

In general, when (FIG. 2) one has to supply a balanced three-phase load,as a stirrer device of the rotary type (11 a), it is necessary to use aninverter (2), provided with three output IGBT branches, that is to say,a first IGBT branch related to the first phase, a second IGBT branchrelated to the second phase, a third IGBT branch related to the thirdphase. In general, when (FIG. 3, FIG. 4, FIG. 7) one has to supply anunbalanced three-phase load, as a stirrer device of the linear type (11b), it is necessary to use an inverter (2) provided with three outputIGBT branches, that is to say, a first IGBT branch related to the firstphase, a second IGBT branch related to the second phase, a third IGBTbranch related to the third phase and further provided with a fourthoutput IGBT branch. In this case the fourth phase related to the fourthoutput IGBT branch must be connected to the neutral conductor of theload (star point).

By modifying the current and the frequency applied to the stirrer orelectromagnetic stirrer device (1, 1′, 1″, 1′″, 1″″, 11 a, 11 b) bymeans of the inverter (2) an electromagnetic field is generated, whichacts with different stirring force and speed on the metallic material inthe molten state of the rod (16) being formed. In this way it ispossible to apply this force to the metallic material in the moltenstate during the casting phase. The force applied to the metallicmaterial in the molten state by the stirrer or electromagnetic stirrerdevice will provide greater quality to the rod once the final producthas been obtained.

The control device (5), which is in the control stage (6) inside theinverter (2, 2′, 2″, 2′″, 2″″), can work normally with a currentfeedback signal, which is obtained by means (FIG. 7) of a current sensor(27), for example inside the inverter. The current feedback signal maybe compared with a corresponding current reference I-reference which canrange between an I-minimum value=0 and an I-nominal value which definesthe nominal working current for the inverter (2, 2′, 2″, 2′″, 2″″). Fromthe comparison between the current feedback signal and the correspondingcurrent reference a current error signal is obtained, which is sent to acurrent regulator which increases or decreases the output voltage of theinverter (2, 2′, 2″, 2′″, 2″″) in such a way as to obtain an outputcurrent equal to the corresponding current reference I-reference. Thecontrol device (5) uses a vector control which is able to provide highprecision in the adjustment of the current supplied by the inverter (2,2′, 2″, 2′″, 2″″) with great stability.

The working parameters of the inverter can be modified by an operatorpanel or computer with a dedicated program. The inverter can workaccording to different modes, such as a service mode in which commandsand references are set through the operator panel, a control mode bymeans of digital and analogue inputs in which commands and referencesare set through such inputs, a control mode by means of a serialcommunication line controllable by a programmable control device.

In general, the inverter can provide at the output a three-phase voltagein which each phase can have a frequency variable between a minimumdriving frequency Fmin and a maximum driving frequency Fmax. Theinverter (2, 2′, 2″, 2′″, 2″″) can be configured and structured toprovide at the output a driving current ranging between an I-minimumvalue=0 and an I-nominal value which can be selected depending on thecharacteristics of the stirrer or electromagnetic stirrer device. By wayof example and without limitation for the purposes of the presentinvention the currents of generation of the electromagnetic field can bealternating currents having a frequency between 1 and 50 Hertz andintensity between 100 and 1000 amperes. In general, the invertercomprises different commands. For example the inverter comprises apre-charge activation command following which the control device (5)closes a pre-charge contactor until reaching a voltage of the DC buswhich is at least equal to a pre-charge value, in general about 80% ofthe final value. When the pre-charge value has been reached, the controldevice (5) closes a main contactor and the pre-charge phase ends.

In this case the inverter goes into a state corresponding to aready-to-start condition. The inverter further comprises a startcommand, which can be sent when the inverter is in the ready-to-startstate. When the start command is given, the inverter goes into thestarted condition and begins the modulation of the output voltage,providing it with the required value to obtain the required outputvoltage through the space-vector modulator. In this way it is possibleto obtain an output voltage from the inverter equal to 96% of the inputvoltage. The inverter comprises a stop command following which theinverter performs a descending voltage ramp at the end of which itdisables the power applied to the stirrer, returning to the statecorresponding to a ready-to-start condition. The inverter comprises apre-charge deactivation command following which the control device (5)of the control stage (6) of the inverter opens the main contactor. Inthis case the inverter goes into a non-ready-to-start state. Theinverter comprises a start command of an alternate cycle operating mode.In this alternate cycle operating mode, the supplied current is notalways equal to the desired current reference, but the supplied currentpasses from a positive cycle in which the electromagnetic field rotatesin a first direction of rotation, for example clockwise, for a givenspecifiable first period to a negative cycle in which theelectromagnetic field rotates in a second direction of directionopposite to the first direction, for example counter-clockwise, for agiven specifiable second period.

The control device (5) of the control stage (6) of the inverter alsoperforms a monitoring of the unbalance of the supplied currents relativeto the different phases. If the measured current differs from the setone by a value higher than a given alarm threshold, for example thirtyamperes, for a time longer than a given alarm time interval, for examplefifteen seconds, an alarm signal is generated. If the measured currentdiffers from the set one by a value higher than a given breakdownthreshold, for example fifty amperes, for a time longer than a givenbreakdown time interval, for example twenty seconds, a breakdown signalis generated. By means of said monitoring system it is possible tocontrol whether the stirrer or its connection cables are in criticalconditions, such as malfunctions or breakdowns.

In general the inverter comprises a control stage (6) and a power stage(26) which in its turn comprises an AC/DC converter for conversion fromAC voltage to DC voltage and a DC/AC converter for conversion from DCvoltage to AC voltage. Such parts are assembled in one single apparatusin such a way that the inverter can be considered as an AC/AC converter.For example (FIG. 2) a three-phase inverter (2) suitable for the drivingof a stirrer of the rotary type (11 a) can comprise the control stage(6) and the power stage (26) which is configured and structured to drivea first coil (20′), a second coil (20″) and a third coil (20′″) of theelectromagnetic stirrer device of the rotary type (11 a). For example(FIG. 3) a three-phase inverter (2) suitable for the driving of astirrer of the linear type (11 b) can comprise the control stage (6) andthe power stage (26) which is configured and structured to drive a firstcoil (20′), a second coil (20″) and a third coil (20′″) of theelectromagnetic stirrer device of the linear type (11 b). In this casethe inverter (2) is provided with a fourth branch connected to theunbalanced three-phase load consisting of the electromagnetic stirrerdevice of the linear type (11 b).

As explained, the stirrers or electromagnetic stirrer devices commonlyused in the practice are rotary electromagnetic stirrer devices (11 a)and linear electromagnetic stirrer devices (11 b). With particularreference to a linear electromagnetic stirrer device (11 b), it uses anelectromagnetic field that is varied linearly along a longitudinaldevelopment axis of the linear electromagnetic stirrer device (11 b).With particular reference to a rotary electromagnetic stirrer device (11a), it uses an electromagnetic field rotating around a longitudinaldevelopment axis of the rotary electromagnetic stirrer device (11 a).Both the rotary electromagnetic stirrer device (11 a) and the linearelectromagnetic stirrer device (11 b) perform an action of mixing of themolten metal of the partially solidified metallic material rod (16)being produced.

In the linear electromagnetic stirrer device (1, 1′, 1″, 1′″, 1″″, 11 b)the coils (20′, 20″, 20″) are arranged (FIG. 9, FIG. 10, FIG. 11, FIG.12) in line one after the other along a longitudinal development axis(23) of the linear electromagnetic stirrer device (1, 1′, 1″, 1′″, 1″″,11 b). For example one can provide solutions of a linear electromagneticstirrer device (1, 1′, 1″, 1′″, 1″″, 11 b) provided with a first coil(20′), a second coil (20″), a third coil (20″). When these coils (20′,20″, 20″) are supplied by a three-phase current the result which isobtained is a moving electromagnetic field. The electromagnetic fieldthat varies in time induces induced currents in the molten metal of thepartially solidified metallic material rod (16) being produced. Saidinduced currents react with the electromagnetic field giving rise toforces which set in motion the molten metal of the partially solidifiedmetallic material rod (16) being produced, generating a flow of moltenmetal. A strong flow of molten metal generates strong shear stresses andthe shear forces break the dendritic formations near the solid-liquidinterface of the partially solidified metallic material rod (16) beingproduced.

In a rotary stirrer or electromagnetic stirrer device (11 a) there aregenerally six coils which are arranged in space at 60° angles withrespect to each other around the mould. The opposite coils arereciprocally connected in anti-series in such a way as to generate afield which generates a force acting in the same direction. Theresulting electrical phase shift relative to the three command phases ofthe coils is, therefore, of 120° in such a way that the rotaryelectromagnetic stirrer device (11 a) is excited by a three-phasecurrent with a phase shift of 120°. The load is thus balanced.

In a linear stirrer or electromagnetic stirrer device (11 b), on theother hand, the windings of the coils (20′, 20″, 20′″) are arranged(FIG. 9) on one single plane (24) according to a configuration in whichthe coils (20′, 20″, 20′″) are placed in line one after the other alonga longitudinal development axis (23) of the electromagnetic stirrerdevice. The supply is carried out with a three-phase currentphase-shifted by 120°. Due to the non-symmetry of the linear stirrer orelectromagnetic stirrer device (11 b) the load is unbalanced. With aclassic three-phase inverter it is not possible to manage an unbalancedload without introducing an unbalance in the currents as well. To obtaina sinusoidal three-phase current with the same amplitude phase-shiftedby 120° it is necessary to use a special 3-phase inverter provided witha fourth branch and the connection occurs in such a way that the fourthphase related to the fourth output branch is connected to the neutralconductor of the load, that is to say, to the star point of connectionof the coils (20′, 20″, 20′″). The main characteristic of a three-phaseinverter with the additional branch for neutral is to be able to manageunbalanced loads.

With particular reference (FIG. 3, FIG. 4, FIG. 7) to the power stage(26) of the IGBT type of the inverter (2), the connection with thelinear electromagnetic stirrer device (11 b) occurs according to aconfiguration in which multiple connection branches are used. A firstoutput branch of the inverter (2) of a first phase is connected to afirst end of a first coil (20′) of the linear electromagnetic stirrerdevice (11 b). A second output branch of the inverter (2) of a secondphase is connected to a first end of a second coil (20″) of the linearelectromagnetic stirrer device (11 b). A third output branch of theinverter (2) of a third phase is connected to a first end of a thirdcoil (20″) of the linear electromagnetic stirrer device (11 b). A fourthoutput branch of the inverter (2) of a fourth phase is connected to thestar point of the coils (20′, 20″, 20′″), that is to say, the fourthbranch of the inverter (2) is connected to the second end of the firstcoil (20′) and to the second end of the second coil (20″) and to thesecond end of the third coil (20′) of the linear electromagnetic stirrerdevice (11 b). This architecture allows to produce a balanced outputcurrent also in unbalanced load conditions, as in the case of anelectromagnetic stirrer device of the linear type (11 b). Thearchitecture of the three-phase inverter (2) and the connection diagramin the case (FIG. 3, FIG. 4, FIG. 7) of a linear electromagnetic stirrerdevice (11 b) are similar to the architecture of the three-phaseinverter (2) and connection diagram in the case (FIG. 2) of a rotaryelectromagnetic stirrer device (11 a), but in the case (FIG. 3, FIG. 4,FIG. 7) of a linear electromagnetic stirrer device (11 b) there is thefourth output branch of the inverter (2) of a fourth phase which isconnected either to the positive conductor of the DC link or to thenegative one, providing the flexibility to control the neutralpotential, and, therefore, produce a balanced voltage on the loadconsisting of the linear electromagnetic stirrer device (11 b) which initself is not a balanced load, thanks to the presence of a fourth IGBTbranch that controls the star point. For example when (FIG. 4) anunbalanced load, such as a linear electromagnetic stirrer device (11 b),is connected to the inverter (2) provided with a fourth output branch ofa fourth phase with a 3D SVPWM (space vector pulse width modulation)control algorithm, one obtains (FIG. 5, FIG. 6) a balance which ishighlighted by the voltage (FIG. 5) and current (FIG. 6) waveforms onthe unbalanced load.

As previously explained (FIG. 7), the control device (5), which is inthe control stage (6) inside the inverter (2), can work with a currentfeedback signal, which is obtained by means (FIG. 7) of a current sensor(27), for example inside the inverter (2) itself. The current feedbacksignal is compared with a corresponding current reference and the soobtained current error signal is sent to a current regulator whichincreases or decreases the output voltage of the inverter (2) in such away as to obtain an output current equal to the corresponding currentreference. The control device (5) uses a vector control which is able toprovide high precision in the adjustment of the current supplied by theinverter (2) with great stability.

For example, for the purposes of the present invention one can useinverters (2) of the AC/AC type with a load with a maximum power factorof 0.2 or 0.3. For example, one can use inverters with a maximum powerfactor of 0.2 suitable to work with voltages at the input of thecorresponding (FIG. 3) power supply input (3) between 360 and 480 Vac,nominal output current between 400 and 800 Arms, such as 400, 550, 750,800 Arms, with powers between 60 and 120 kW, such as 60, 70, 80, 100,120, 140 kW. For example, one can use inverters with a maximum powerfactor of 0.2 suitable to work with voltages at the input of thecorresponding (FIG. 3) power supply input (3) between 540 and 660 Vac,nominal output current between 400 and 800 Arms, such as 400, 550, 750,800 Arms, with powers between 90 and 210 kW, such as 90, 110, 120, 150,180, 210 kW. For example, one can use inverters with a maximum powerfactor of 0.3 suitable to work with voltages at the input of thecorresponding (FIG. 3) power supply input (3) between 360 and 480 Vac,nominal output current between 400 and 800 Arms, such as 400, 550, 750,800 Arms, with powers between 90 and 210 kW, such as 90, 110, 120, 150,180, 210 kW. For example, one can use inverters with a maximum powerfactor of 0.3 suitable to work with voltages at the input of thecorresponding (FIG. 3) power supply input (3) between 540 and 660 Vac,nominal output current between 400 and 800 Arms, such as 400, 550, 750,800 Arms, with powers between 130 and 320 kW, such as 130, 160, 180, 220285, 320 kW.

The inverters (2) may be provided with further auxiliary power supplyinputs for the electronics of the power module at 110 or 220 Vac, or fordigital inputs at 24 Vdc.

Inverters (2) suitable for the present invention can have an IGBTswitching frequency between 0.5 and 1.5 kHz, such as 0.5, 0.75, 1.0,1.25, 1.5 kHz.

For example (FIG. 9, FIG. 10), consider a casting machine which isconfigurable according to two operating configurations. In the firstoperating configuration (FIG. 9) of the casting machine one singleproduct is cast in one single mould (14) under the stirring action ofthe molten bath by means of four linear stirrers (1′, 1″, 1′″, 1″″)comprising a first stirrer device (1′), a second stirrer device (1″), athird stirrer device (1″), a fourth stirrer device (1″″). In the secondoperating configuration (FIG. 10) of the casting machine two productsare simultaneously cast in two moulds (14′, 14″) under the stirringaction of the molten bath by means of four linear stirrers (1′, 1″, 1′″,1″″). The two products are cast on parallel casting lines of the samemachine under the stirring action of the molten bath by means of twolinear stirrers for each casting line; the casting machine is thusprovided with a first mould (14′) and with a second mould (14″). Thefirst mould (14′) is subjected to the action of one pair of the linearstirrers (1′, 1″) comprising a first stirrer device (1′), a secondstirrer device (1″). The second mould (14″) is subjected to the actionof another pair of linear stirrers (1″, 1″″) comprising a third stirrerdevice (1″), a fourth stirrer device (1″).

Each of the stirrer devices (1′, 1″, 1′″, 1″″), that is to say, thefirst stirrer device (1′), the second stirrer device (1″), the thirdstirrer device (1″), the fourth stirrer device (1″″), is a stirrerdevice of the linear type comprising at least two coils (20′, 20″,20′″), preferably comprising a first coil (20′), a second coil (20″), athird coil (20′″) which are arranged in line one after the other along alongitudinal development axis (23) of the linear electromagnetic stirrerdevice according to a configuration in which the windings of the coils(20′, 20″, 20′″) are arranged (FIG. 9) on one single plane (24) which isparallel to the longitudinal development axis (23) of the linearelectromagnetic stirrer device.

The use of the linear stirrers in pairs or in a configuration with fourstirrers is aimed at particular types of casting machines in which thesmallest formats of produced metal rod (16) can be cast simultaneouslyon two parallel lines while the largest formats of produced metal rod(16) are cast in one single central line which is in a central positionof the casting machine with respect to the position of the two parallellines adopted for the small formats. For example, and without limitationfor the purposes of the present invention, by the expression “smallformats” one means metal rods (16) produced with a circular section anddiameters between 400 and 1000 mm. For example, and without limitationfor the purposes of the present invention, by the expression “largeformats” one means metal rods (16) produced with a circular section anddiameters between 1000 and 1600 mm.

Resorting to a simplified single line representation (FIG. 8) theconnection of the stirrer devices (1′, 1″, 1′″, 1″″) to the supplynetwork occurs by means of one single transformer (12) which supplies adistribution panel (10) supplying each of the inverters (2′, 2″, 2′″,2″″) which supplies a respective stirrer device (1′, 1″, 1′″, 1″″) bymeans of connection boxes (9, 9′, 9″, 9′″, 9″″). In particular, thefirst stirrer device (1′) is connected to the first inverter (2′),preferably through a first connection box (9′), the second stirrerdevice (1″) is connected to the second inverter (2″), preferably througha second connection box (9″), the third stirrer device (1′″) isconnected to the third inverter (2′″), preferably through a thirdconnection box (9′″), the fourth stirrer device (1″″) is connected tothe fourth inverter (2″″), preferably through a fourth connection box(9″″). The first inverter (2′), the second inverter (2″), the thirdinverter (2′″) and the fourth inverter (2″″) are connected to thedistribution panel (10) with the interposition of further devices, suchas contactors (13) or disconnectors (17).

Both in the case in which the casting machine is configured to operatein the first operating configuration (FIG. 9) with the casting of onesingle product in one single mould (14), and in the case in which thecasting machine is configured to operate in the second operatingconfiguration (FIG. 10) with the casting of two products in two moulds(14′, 14″), pairs of stirrers or stirrer devices (1′, 1″, 1′″, 1″″)opposite with respect to the central axis of the mould (14, 14′, 14″)can be configured in such a way that:

-   -   one of the stirrer devices (1′, 1″, 1′″, 1″″) of said pair        exerts on the molten metal in the mould (14, 14′, 14″) a force        which is oriented in the same direction (FIG. 11) with respect        to the other one of the stirrer devices (1′, 1″, 1′″, 1″″) of        said pair of opposite stirrers or stirrer devices (1′, 1″, 1′″,        1″″). For example (FIG. 11) a first stirrer device (1′) of said        pair exerts on the molten metal a force which is essentially        oriented upwards and a second stirrer device (1″) of said pair        exerts on the molten metal a force which is essentially oriented        upwards.

For example a first stirrer device (1′) of said pair exerts on themolten metal a force which is essentially oriented downwards and asecond stirrer device (1″) of said pair exerts on the molten metal aforce which is essentially oriented downwards;

-   -   one of the stirrer devices (1′, 1″, 1′″, 1″″) of said pair        exerts on the molten metal in the mould (14, 14′, 14″) a force        which is oriented in the opposite direction (FIG. 12) with        respect to the other one of the stirrer devices (1′, 1″, 1′″,        1″″) of said pair of opposite stirrers or stirrer devices (1′,        1″, 1′″, 1″″). For example (FIG. 12) a first stirrer device (1′)        of said pair exerts on the molten metal a force which is        essentially oriented upwards and a second stirrer device (1″) of        said pair exerts on the molten metal a force which is        essentially oriented downwards. The terms “upwards” and        “downwards” refer to the direction of the force of gravity when        the mould (14) is installed in an essentially vertical        condition. It will be obvious that similar considerations, with        adaptations that will be obvious for a person skilled in the        art, also apply in the case of a mould arranged inclined with        respect to the direction of the force of gravity.

With particular reference to the case in which the casting machine isconfigured to operate in the first operating configuration (FIG. 9) withthe casting of one single product in one single mould (14), it can beprovided that four stirrers or stirrer devices (1′, 1″, 1′″, 1″″) act aslinear stirrers on the molten metal of the mould according to alternateconfigurations. For example (FIG. 9) in the sequence of four stirrerdevices (1′, 1″, 1′″, 1″″) arranged around the mould each stirrer devicecan be configured in such a way as to exert on the molten metal a forcewhich is oriented according to an essentially vertical direction whichis an opposite direction with respect to the essentially verticaldirection according to which the force exerted by the other stirrerdevices adjacent thereto in the sequence of four stirrer devices (1′,1″, 1′″, 1″″) arranged around the mould is oriented. According to thisconfiguration, for example (FIG. 9), the stirrer devices (1′, 1″, 1′″,1″″) may be configured and structured in such a way as to operateaccording to:

-   -   a first operating mode in which the first stirrer device (1′)        exerts on the molten metal a force which is essentially oriented        upwards, the third stirrer device (1′″) exerts on the molten        metal a force which is essentially oriented downwards, the        second stirrer device (1″) exerts on the molten metal a force        which is essentially oriented upwards, the fourth stirrer device        (1″″) exerts on the molten metal a force which is essentially        oriented downwards;

or

-   -   a second operating mode in which the first stirrer device (1′)        exerts on the molten metal a force which is essentially oriented        downwards, the third stirrer device (1′″) exerts on the molten        metal a force which is essentially oriented upwards, the second        stirrer device (1″) exerts on the molten metal a force which is        essentially oriented downwards, the fourth stirrer device (1″″)        exerts on the molten metal a force which is essentially oriented        upwards;

or

-   -   a third operating mode in which one alternates time periods in        which the stirrer devices (1′, 1″, 1′″, 1″″) operate in        accordance with the first operating mode and time periods in        which the stirrer devices (1′, 1″, 1′″, 1″″) operate in        accordance with the second operating mode;    -   a fourth operating mode in which one alternates time periods in        which only a first pair of stirrer devices (1′, 1″, 1′″, 1″″)        reciprocally opposite with respect to the central axis of the        mould (14, 14′, 14″) operates and time periods in which only a        second pair of stirrer devices (1′, 1″, 1′″, 1″″) reciprocally        opposite with respect to the central axis of the mould (14, 14′,        14″) operates, which is different from the first pair. For        example (FIG. 9) the first stirrer device (1′) and the second        stirrer device (1″) can operate in a first period while the        third stirrer device (1′″) and the fourth stirrer device (1″″)        are off and the third stirrer device (1′″) and the fourth        stirrer device (1″″) can operate in a second period, which is        subsequent to the first period, while the first stirrer device        (1′) and the second stirrer device (1″) are off.

The terms “upwards” and “downwards” refer to the direction of the forceof gravity when the mould (14) is installed in an essentially verticalcondition. It will be obvious that similar considerations, withadaptations that will be obvious for a person skilled in the art, alsoapply in the case of a mould arranged inclined with respect to thedirection of the force of gravity.

It should be noted that the solution according to the invention ischaracterized by great flexibility of use. In fact, with particularreference to the case in which the casting machine is configured tooperate in the first operating configuration (FIG. 9) with the castingof one single product in one single mould (14) which comprises fourstirrer devices (1′, 1″, 1′″, 1″″) each of which is configured as alinear stirrer and provided with at least one pair of coils (20′, 20″,20′″), it may be provided that the four stirrer devices (1′, 1″, 1′″,1″″) work all together, each driven by the respective inverter (2′, 2″,2′″, 2″″) equipped with the fourth output branch connected to theneutral conductor of the load, that is to say, to the star point ofconnection of the coils (20′, 20″, 20′″) according to two possibleconfigurations which are defined in the following as operatingconfiguration with a fourth compensation branch or single-coil operatingconfiguration. In both configurations, one inverter is configured as amaster inverter and the other three inverters are configured as slaveinverters.

In case of an operating configuration with a fourth compensation branch,the fourth branch of the inverter, connected to the star point of therespective stirrer device (1′, 1″, 1′″, 1″″), is used to compensate forthe unbalanced currents which are created due to the linear typology ofthe stirrer, as the currents in the three phases are different in theeffective value because the geometry of the stirrer creates mutualinductances which are different in the different phases. In thisoperating configuration all the coils (20′, 20″, 20′″) of each stirrerdevice (1′, 1″, 1′″, 1″″) are supplied similarly to a three-phase rotarystirrer creating a pushing flow, which is oriented upwards or downwards.Preferably in this case the stirrer devices (1′, 1″, 1′″, 1″″) are usedin pairs according to a configuration in which each stirrer forms a pairwith the diametrically opposite one and each pair is alternativelyactivated for a given time interval, in accordance with the previouslydefined fourth operating mode in which one alternates time periods inwhich only a first pair of stirrer devices (1′, 1″, 1′″, 1″″)reciprocally opposite with respect to the central axis of the mould (14,14′, 14″) operates and time periods in which only a second pair ofstirrer devices (1′, 1″, 1′″, 1″″) reciprocally opposite with respect tothe central axis of the mould (14, 14′, 14″) operates, which isdifferent from the first pair. The motion induced in the molten metaloccurs along the casting axis. The stirrers forming a pair can work withthe same sequence of phases (FIG. 11) or with an inverted sequence ofphases between one stirrer and the other (FIG. 12), in accordance withwhat has been outlined above.

In case of a single-coil operating configuration, preferably, only onecoil (20′, 20″, 20′″) of each stirrer device (1′, 1″, 1′″, 1″″) issupplied. For example, one can use only the first coils (1′) of thefirst stirrer device (1′), second stirrer device (1″), third stirrerdevice (1′″) and fourth stirrer device (1″″). In the case in which oneonly uses the coils which are placed in a closer position with respectto the beginning of the mould (14), that is to say, closer to the zonein which the molten metal is cast, which in the exemplary embodiment(FIG. 9) are the first coils (20′), one obtains an effect similar tothat of a rotary stirrer mounted in the highest position of the mould.In the case in which one only uses the coils which are placed in acloser position with respect to the end of the mould (14), that is tosay, closer to the exit zone of the metal rod (16) from the mould, whichin the exemplary embodiment (FIG. 9) are the third coils (20′″), oneobtains an effect similar to that of a rotary stirrer mounted in thelowest position of the mould. In the case in which one only uses thecoils which are placed in an intermediate position with respect to theprevious ones, which in the exemplary embodiment (FIG. 9) are the secondcoils (20″), one obtains an effect similar to that of a rotary stirrermounted in the intermediate position of the mould. Advantageously,however, the use of such three different rotary stirring modes can bevaried as desired during the casting process without it being necessaryto change the position of the stirrer within the mould, which can occuronly with the machine stopped and the mould open. Each inverter drivesonly one coil by using the fourth branch of the inverter, connected tothe star point of the respective stirrer device (1′, 1″, 1′″, 1″″), forthe return current and in each stirrer the current will be phase-shiftedby 90° with respect to that of the previous or following stirrer,enabling the clockwise or anti-clockwise rotation of the electromagneticfield. In this mode the movement induced in the molten metal is rotarywith an axis parallel to that of casting, as in the application of therotary stirrers.

In practice, with particular reference to the case in which the castingmachine is configured to operate in the first operating configuration(FIG. 9) with the casting of one single product in one single mould(14), with the described configurations it is possible to pass, asdesired, and during a same casting process as well, from a stirringcondition of the rotary type to a stirring condition of the linear type.

Considering now the case in which the casting machine is configured tooperate in the second operating configuration (FIG. 10) with the castingof two products in two moulds (14′, 14″), one obtains that a first mould(14′) is subjected to the action of one pair of the linear stirrers (1′,1″) comprising a first stirrer device (1′), a second stirrer device (1″)and a second mould (14″) is subjected to the action of another pair oflinear stirrers (1′″, 1″″) comprising a third stirrer device (1′″), afourth stirrer device (1″″). In this case the only operatingconfiguration available is the one with a fourth compensation branch. Infact, the single-coil operating configuration, which has been previouslydescribed to obtain a stirring effect similar to that of a rotarystirrer, is not applicable because, there being only two stirrers foreach mould (14′, 14″), the activation of only one coil for each stirrerwould not produce any rotary motion in the molten metal. In particular,considering only, for simplicity, the first mould (14′) and consideringthat for the second mould (14″) completely similar considerations apply,one can provide:

-   -   a first operating mode (FIG. 11) in which the first stirrer        device (1′) exerts on the molten metal a force which is        essentially oriented upwards, the second stirrer device (1″)        exerts on the molten metal a force which is essentially oriented        upwards;

or

-   -   a second operating mode in which the first stirrer device (1′)        exerts on the molten metal a force which is essentially oriented        downwards, the second stirrer device (1″) exerts on the molten        metal a force which is essentially oriented downwards;

or

-   -   a third operating mode (FIG. 12) in which the first stirrer        device (1′) exerts on the molten metal a force which is        essentially oriented upwards, the second stirrer device (1″)        exerts on the molten metal a force which is essentially oriented        downwards or vice versa;

or

-   -   a fourth operating mode in which one alternates first time        periods in which the stirrer devices (1′, 1″) operate in        accordance with one of a first operating mode, a second        operating mode, a third operating mode, and second time periods        in which the stirrer devices (1′, 1″) operate in accordance with        an operating mode which is different from that of the first        period and is selected from first operating mode, second        operating mode, third operating mode.

The terms “upwards” and “downwards” refer to the direction of the forceof gravity when the mould (14) is installed in an essentially verticalcondition. It will be obvious that similar considerations, withadaptations that will be obvious for a person skilled in the art, alsoapply in the case of a mould arranged inclined with respect to thedirection of the force of gravity.

In the case of a casting machine which is configured to operate in thesecond operating configuration (FIG. 10) and operating configurationwith a fourth compensation branch, all the coils (20′, 20″, 20′″) ofeach stirrer device (1′, 1″, 1′″, 1″″) are supplied similarly to thethree-phase rotary stirrers and each stirrer device (1′, 1″, 1′″, 1″″)is coupled with a corresponding stirrer device (1′, 1″, 1′″, 1″″) whichis on the opposite side of the respective mould (14′, 14″). The motioninduced in the molten metal is along the casting axis. Both stirrerdevices of one pair can work in phase (FIG. 11) or out of phase (FIG.12).

The pair of stirrer devices (1′, 1″) operating on the first mould (14′)is independent from the pair of stirrer devices (1′″, 1″″) operating onthe second mould (14″) and each casting line can be started or stoppedindependently of the status of the other line.

In the case of a casting machine which can pass from the first operatingconfiguration (FIG. 9) to the second operating configuration (FIG. 10)and vice versa, therefore, one will have:

-   -   a first configuration in which (FIG. 9) the stirrers or stirrer        devices (1′, 1″, 1′″, 1″″) operate on one single mould (14)        according to what has been previously described with reference        to the first operating configuration (FIG. 9). In particular in        the operating configuration with a fourth compensation branch        the corresponding pairs of stirrers will be (FIG. 9) a first        pair (1′, 1″) and a second pair (1′″, 1″″);    -   a second configuration in which (FIG. 10) the stirrers or        stirrer devices (1′, 1″, 1′″, 1″″) operate on a first mould        (14′) and a second mould (14″) according to what has been        previously described with reference to the second operating        configuration (FIG. 10). In order to pass from the previous        configuration (FIG. 9) to this one (FIG. 10), the stirrers are        rotated and moved into the new position. In particular, in the        operating configuration with a fourth compensation branch the        corresponding pairs of stirrers will be (FIG. 10) a first pair        (1′, 1″) and a second pair (1′″, 1″″).

In any casting configuration, first configuration (FIG. 9) with onesingle mould (14) or second configuration (FIG. 10) with two moulds(14′, 14″) a master inverter is able to control the other slaveinverters independently of one another, coupling them according to whatis required by the configuration of the casting machine.

Therefore, by the solution according to the invention one will havedifferent operating modes according to what is summarized in thefollowing tables.

TABLE 1 Direction of the Casting Stirrer 1′ Stirrer 1″ Stirrer 1′″Stirrer 1″″ force exerted by lines Operating Master Slave Slave Slavethe field config. configuration (20′″/20″/20′) (20′″/20″/20′)(20′″/20″/20′) (20′″/20″/20′) 1′ 1″ 1′″ 1″″ 1 Line (FIG. 9) 0 singlecoil 0°/—/— 180°/—/— 90°/—/— 270°/—/—

 or  

1 4^(th) compens. 0°/120°/240° 0°/120°/240° —/—/— —/—/— ↑ ↑ — — branch—/—/— —/—/— 0°/120°/240° 0°/120°/240° — — ↑ ↑ 2 4^(th) compens.0°/120°/240° 240°/120°/0° —/—/— —/—/— ↑ ↓ — — branch —/—/— —/—/—0°/120°/240° 240°/120°/0° — — ↑ ↓

In the operating configurations indicated by “0”, “1”, “2” in table 1the casting machine operates in the first operating configuration (FIG.9) in which one single product is cast in one single mould (14) underthe stirring action of the molten bath by means of four linear stirrersor stirrer devices (1′, 1″, 1′″, 1″″) which are arranged around themould (14) at ninety-degree angles with respect to each other and,proceeding clockwise (FIG. 9) in the following order: first stirrerdevice (1′), third stirrer device (1′″), second stirrer device (1″),fourth stirrer device (1″″).

In the operating configuration indicated by “0” the stirrer devices (1′,1″, 1′″, 1″″) are controlled according to a single-coil operatingconfiguration in which, preferably but not necessarily, only one coil(20′, 20″, 20′″) of each stirrer device (1′, 1″, 1′″, 1″″) is supplied.

Each inverter drives one single coil by using the fourth branch of theinverter, connected to the star point of the respective stirrer device(1′, 1″, 1′″, 1″″), for the return current and in each stirrer thecurrent will be phase-shifted by 90° with respect to that of theprevious or following stirrer, enabling the clockwise or anti-clockwiserotation of the electromagnetic field. In this mode the movement inducedin the molten metal is rotary with an axis parallel to that of casting,as in the application of the rotary stirrers. In practice the linearstirrers are controlled in sequence obtaining an effect, on the moltenmetal in the mould (14), similar to that of a rotary stirrer.

In the operating configuration indicated by “1” the stirrer devices (1′,1″, 1′″, 1″″) are controlled according to an operating configurationwith a fourth compensation branch in which the fourth branch of theinverter, connected to the star point of the respective stirrer device(1′, 1″, 1′″, 1″″) is used to compensate for the unbalanced currentswhich are created due to the linear typology of the stirrer. In thisoperating configuration all the coils (20′, 20″, 20′″) of each stirrerdevice (1′, 1″, 1′″, 1″″) are supplied similarly to a three-phase rotarystirrer creating a pushing flow, which is oriented upwards or downwards.Preferably in this case the stirrer devices (1′, 1″, 1′″, 1″″) are usedin pairs according to a configuration in which each stirrer forms a pairwith the diametrically opposite one with respect to the mould (14) andeach pair is alternatively activated for a given time interval, incompliance with the previously defined fourth operating mode in whichone alternates time periods in which only a first pair of stirrerdevices (1′, 1″, 1′″, 1″″) reciprocally opposite with respect to thecentral axis of the mould (14, 14′, 14″) operates and time periods inwhich only a second pair of stirrer devices (1′, 1″, 1′″, 1″″)reciprocally opposite with respect to the central axis of the mould (14,14′, 14″) operates, which is different from the first pair. In thespecific case of the operating configuration indicated by “1”, a firstpair of stirrer devices (1′, 1″, 1′″, 1″″) consisting of a first stirrerdevice (1′) and second stirrer device (1″), which exert both a forcethat is oriented upwards, operates in a first time period, while asecond pair of stirrer devices (1′, 1″, 1′″, 1″″) consisting of a thirdstirrer device (1′″) and fourth stirrer device (1″″), which exert both aforce that is oriented upwards, operates in a second time period.

In the operating configuration indicated by “2” the stirrer devices (1′,1″, 1′″, 1″″) are controlled according to an operating configurationwith a fourth compensation branch in which the fourth branch of theinverter, connected to the star point of the respective stirrer device(1′, 1″, 1′″, 1″″), is used to compensate for the unbalanced currentswhich are created due to the linear typology of the stirrer. In thisoperating configuration all the coils (20′, 20″, 20′″) of each stirrerdevice (1′, 1″, 1′″, 1″″) are supplied similarly to a three-phase rotarystirrer creating a pushing flow, which is oriented upwards or downwards.Preferably in this case the stirrer devices (1′, 1″, 1′″, 1″″) are usedin pairs according to a configuration in which each stirrer forms a pairwith the diametrically opposite one with respect to the mould (14) andeach pair is alternatively activated for a given time interval, incompliance with the previously defined fourth operating mode in whichone alternates time periods in which only a first pair of stirrerdevices (1′, 1″, 1′″, 1″″) reciprocally opposite with respect to thecentral axis of the mould (14, 14′, 14″) operates and time periods inwhich only a second pair of stirrer devices (1′, 1″, 1′″, 1″″)reciprocally opposite with respect to the central axis of the mould (14,14′, 14″) operates, which is different from the first pair. In thespecific case of the operating configuration indicated by “2”, a firstpair of stirrer devices (1′, 1″) consisting of a first stirrer device(1′) and second stirrer device (1″), in which the first stirrer device(1′) exerts a force that is oriented upwards and the second stirrerdevice (1″) exerts a force that is oriented downwards, operates in afirst time period, while a second pair of stirrer devices (1′″, 1″″)consisting of a third stirrer device (1′″) and fourth stirrer device(1″″), in which the third stirrer device (1′″) exerts a force that isoriented upwards and the fourth stirrer device (1″″) exerts a force thatis oriented downwards, operates in a second time period.

TABLE 2 Direction of the Casting Stirrer 1′ Stirrer 1″ Stirrer 1′″Stirrer 1″″ force exerted by lines Operating Master Slave Slave Slavethe field config. configuration (20′″/20″/20′) (20′″/20″/20′)(20′″/20″/20′) (20′″/20″/20′) 1′ 1″ 1′″ 1″″ 2 Lines (FIG. 10) 3 4^(th)compens. 0°/120°/240° 0°/120°/240° —/—/— —/—/— ↑ ↑ — — One line isoperative branch One line is inoperative 4 4^(th) compens. —/—/— —/—/—0°/120°/240° 0°/120°/240° — — ↑ ↑ branch 5 4^(th) compens. 0°/120°/240°240°/120°/0° —/—/— —/—/— ↑ ↓ — — branch 6 4^(th) compens. —/—/— —/—/—0°/120°/240° 240°/120°/0° — — ↑ ↓ branch

In the operating configurations indicated by “3”, “4”, “5”, “6” in table2 the casting machine operates in the second operating configuration(FIG. 10) in which the machine is configured and structured to castsimultaneously two products in two moulds (14′, 14″) under the stirringaction of the molten bath by means of four linear stirrers or stirrerdevices (1′, 1″, 1′″, 1″″). In particular, a first stirrer device (1′)and a second stirrer device (1″) are arranged facing each other onopposite sides of the first mould (14′) and wherein a third stirrerdevice (1′″) and a fourth stirrer device (1″″) are arranged facing eachother on opposite sides of the second mould (14″).

In the operating configuration indicated by “3” only the first mould(14′) related to a first casting line is operative, while the secondmould (14″) related to a second casting line is inoperative in the sensethat no molten metal is cast in it. The first stirrer device (1′) andthe second stirrer device (1″) exert both a force that is orientedupwards.

In the operating configuration indicated by “4” only the second mould(14″) related to a second casting line is operative, while the firstmould (14′) related to a first casting line is inoperative in the sensethat no molten metal is cast in it. The third stirrer device (1′″) andthe fourth stirrer device (1″″) exert both a force that is orientedupwards.

In the operating configuration indicated by “5” only the first mould(14′) related to a first casting line is operative while the secondmould (14″) related to a second casting line is inoperative in the sensethat no molten metal is cast in it. The first stirrer device (1′) exertsa force that is oriented upwards and the second stirrer device (1″)exerts a force that is oriented downwards.

In the operating configuration indicated by “6” only the second mould(14″) related to a second casting line is operative while the firstmould (14′) related to a first casting line is inoperative in the sensethat no molten metal is cast in it. The third stirrer device (1′″)exerts a force that is oriented upwards and the fourth stirrer device(1″″) exerts a force that is oriented downwards.

TABLE 3 Direction of the Casting Stirrer 1′ Stirrer 1″ Stirrer 1′″Stirrer 1″″ force exerted by lines Operating Master Slave Slave Slavethe field config. configuration (20′″/20″/20′) (20′″/20″/20′)(20′″/20″/20′) (20′″/20″/20′) 1′ 1″ 1′″ 1″″ 2 Lines (FIG. 10) 7 4^(th)compens. 0°/120°/240° 0°/120°/240° 0°/120°/240° 0°/120°/240° ↑ ↑ ↑ ↑Both lines are branch operative 8 4^(th) compens. 0°/120°/240°240°/120°/0° 0°/120°/240° 240°/120°/0° ↑ ↓ ↑ ↓ branch 9 4^(th) compens.0°/120°/240° 240°/120°/0° 0°/120°/240° 0°/120°/240° ↑ ↓ ↑ ↑ branch 104^(th) compens. 0°/120°/240° 0°/120°/240° 0°/120°/240° 240°/120°/0° ↑ ↑↑ ↓ branch

In the operating configurations indicated by “7”, “8”, “9”, “10” intable 3 the casting machine operates in the second operatingconfiguration (FIG. 10) in which the machine is configured andstructured to cast simultaneously two products in two moulds (14′, 14″)under the stirring action of the molten bath by means of four linearstirrers or stirrer devices (1′, 1″, 1′″, 1″″). In particular, a firststirrer device (1′) and a second stirrer device (1″) are arranged facingeach other on opposite sides of the first mould (14′) and wherein athird stirrer device (1′″) and a fourth stirrer device (1″″) arearranged facing each other on opposite sides of the second mould (14″).

In the operating configuration indicated by “7” both the first mould(14′) related to a first casting line and the second mould (14″) relatedto a second casting line are operative. On the first mould (14′), thefirst stirrer device (1′) and the second stirrer device (1″) exert botha force that is oriented upwards. On the second mould (14″), the thirdstirrer device (1′″) and the fourth stirrer device (1″″) exert both aforce that is oriented upwards.

In the operating configuration indicated by “8” both the first mould(14′) related to a first casting line and the second mould (14″) relatedto a second casting line are operative. On the first mould (14′), thefirst stirrer device (1′) exerts a force that is oriented upwards andthe second stirrer device (1″) exerts a force that is orienteddownwards. On the second mould (14″), the third stirrer device (1′″)exerts a force that is oriented upwards and the fourth stirrer device(1″″) exerts a force that is oriented downwards.

In the operating configuration indicated by “9” both the first mould(14′) related to a first casting line and the second mould (14″) relatedto a second casting line are operative. On the first mould (14′), thefirst stirrer device (1′) exerts a force that is oriented upwards andthe second stirrer device (1″) exerts a force that is orienteddownwards. On the second mould (14″), the third stirrer device (1′″) andthe fourth stirrer device (1″″) exert both a force that is orientedupwards.

In the operating configuration indicated by “10” both the first mould(14′) related to a first casting line and the second mould (14″) relatedto a second casting line are operative. On the first mould (14′), thefirst stirrer device (1′) and the second stirrer device (1″) exert botha force that is oriented upwards. On the second mould (14″), the thirdstirrer device (1′″) exerts a force that is oriented upwards and thefourth stirrer device (1″″) exerts a force that is oriented downwards.

By the solution according to the invention the operating modes accordingto what is summarized in the following tables are also possible.

TABLE 4 Direction of the Casting Stirrer 1′ Stirrer 1″ Stirrer 1′″Stirrer 1″″ force exerted by lines Operating Master Slave Slave Slavethe field config. configuration (20′″/20″/20′) (20′″/20″/20′)(20′″/20″/20′) (20′″/20″/20′) 1′ 1″ 1′″ 1″″ 1 Line (FIG. 9) 11 4^(th)compens. 240°/120°/0° 240°/120°/0° —/—/— —/—/— ↓ ↓ — — branch —/—/——/—/— 240°/120°/0° 240°/120°/0° — — ↓ ↓ 12 4^(th) compens. 0°/120°/240°0°/120°/240° —/—/— —/—/— ↑ ↑ — — branch —/—/— —/—/— 240°/120°/0°240°/120°/0° — — ↓ ↓ 13 4^(th) compens. 240°/120°/0° 240°/120°/0° —/—/——/—/— ↓ ↓ — — branch —/—/— —/—/— 0°/120°/240° 0°/120°/240° — — ↑ ↑

In the operating configurations indicated by “11”, “12”, “13”, in table4 the casting machine operates in the first operating configuration(FIG. 9) in which one single product is cast in one single mould (14)under the stirring action of the molten bath by means of four linearstirrers or stirrer devices (1′, 1″, 1′″, 1″″) which are arranged aroundthe mould (14) at ninety-degree angles with respect to each other and,proceeding clockwise (FIG. 9) in the following order: first stirrerdevice (1′), third stirrer device (1′″), second stirrer device (1″),fourth stirrer device (1″″). The stirrer devices (1′, 1″, 1′″, 1″″) arecontrolled according to an operating configuration with a fourthcompensation branch in which the fourth branch of the inverter,connected to the star point of the respective stirrer device (1′, 1″,1′″, 1″″), is used to compensate for the unbalanced currents which arecreated due to the linear typology of the stirrer.

In this operating configuration all the coils (20′, 20″, 20′″) of eachstirrer device (1′, 1″, 1′″, 1″″) are supplied similarly to athree-phase rotary stirrer creating a pushing flow, which is orientedupwards or downwards. Preferably in this case the stirrer devices (1′,1″, 1′″, 1″″) are used in pairs according to a configuration in whicheach stirrer forms a pair with the diametrically opposite one withrespect to the mould (14) and each pair is alternatively activated for agiven time interval, in compliance with the previously defined fourthoperating mode in which one alternates time periods in which only afirst pair of stirrer devices (1′, 1″, 1′″, 1″″) reciprocally oppositewith respect to the central axis of the mould (14, 14′, 14″) operatesand time periods in which only a second pair of stirrer devices (1′, 1″,1′″, 1″″) reciprocally opposite with respect to the central axis of themould (14, 14′, 14″) operates, which is different from the first pair.In the specific case of the operating configuration indicated by “11”, afirst pair of stirrer devices (1′, 1″, 1′″, 1″″) consisting of a firststirrer device (1′) and second stirrer device (1″), which exert both aforce that is oriented downwards, operates in a first time period, whilea second pair of stirrer devices (1′, 1″, 1′″, 1″″) consisting of athird stirrer device (1′″) and fourth stirrer device (1″″), which exertboth a force that is oriented downwards, operates in a second timeperiod. In the specific case of the operating configuration indicated by“12”, a first pair of stirrer devices (1′, 1″, 1′″, 1″″) consisting of afirst stirrer device (1′) and second stirrer device (1″), which exertboth a force that is oriented upwards, operates in a first time period,while a second pair of stirrer devices (1′, 1″, 1′″, 1″″) consisting ofa third stirrer device (1′″) and fourth stirrer device (1″″), whichexert both a force that is oriented downwards, operates in a second timeperiod.

In the specific case of the operating configuration indicated by “13”,the situation is similar to that described for the operatingconfiguration indicated by “12” with the difference that the first pairof stirrer devices (1′, 1″, 1′″, 1″″) consisting of a first stirrerdevice (1′) and second stirrer device (1″), which exert both a forcethat is oriented downwards, operates in the first time period, while thesecond pair of stirrer devices (1′, 1″, 1′″, 1″″) consisting of a thirdstirrer device (1′″) and fourth stirrer device (1″″), which exert both aforce that is oriented upwards, operates in the second time period.

TABLE 5 Direction of the Casting Stirrer 1′ Stirrer 1″ Stirrer 1′″Stirrer 1″″ force exerted by lines Operating Master Slave Slave Slavethe field config. configuration (20′″/20″/20′) (20′″/20″/20′)(20′″/20″/20′) (20′″/20″/20′) 1′ 1″ 1′″ 1″″ 2 Lines (FIG. 10) 14 4^(th)compens. 240°/120°/0° 240°/120°/0° —/—/— —/—/ ↓ ↓ — — One line isoperative branch One line is inoperative 15 4^(th) compens. —/—/— —/—/—240°/120°/0° 240°/120°/0° — — ↓ ↓ branch

In the operating configurations indicated by “14”, “15” in table 5 thecasting machine operates in the second operating configuration (FIG. 10)in which the machine is configured and structured to cast simultaneouslytwo products in two moulds (14′, 14″) under the stirring action of themolten bath by means of four linear stirrers or stirrer devices (1′, 1″,1′″, 1″″). In particular, a first stirrer device (1′) and a secondstirrer device (1″) are arranged facing each other on opposite sides ofthe first mould (14′) and wherein a third stirrer device (1′″) and afourth stirrer device (1″″) are arranged facing each other on oppositesides of the second mould (14″).

In the operating configuration indicated by “14” only the first mould(14′) related to a first casting line is operative while the secondmould (14″) related to a second casting line is inoperative in the sensethat no molten metal is cast in it. The first stirrer device (1′) andthe second stirrer device (1″) exert both a force that is orienteddownwards.

In the operating configuration indicated by “15” only the second mould(14″) related to a second casting line is operative while the firstmould (14′) related to a first casting line is inoperative in the sensethat no molten metal is cast in it. The third stirrer device (1′″) andthe fourth stirrer device (1″″) exert both a force that is orienteddownwards.

TABLE 6 Direction of the Casting Stirrer 1′ Stirrer 1″ Stirrer 1′″Stirrer 1″″ force exerted by lines Operating Master Slave Slave Slavethe field Config. configuration (2′″/20″/20′) (2′″/20″/20′)(2′″/20″/20′) (2′″/20″/20′) 1′ 1″ 1′″ 1″″ 2 Lines (FIG. 10) 16 4^(th)compens. 240°/120°/0° 240°/120°/0° 240°/120°/0° 240°/120°/0° ↓ ↓ ↓ ↓Both lines are branch operative 17 4^(th) compens. 0°/120°/240°0°/120°/240° 240°/120°/0° 240°/120°/0° ↑ ↑ ↓ ↓ branch 18 4^(th) compens.240°/120°/0° 240°/120°/0° 0°/120°/240° 0°/120°/240° ↓ ↓ ↑ ↑ branch

In the operating configurations indicated by “16”, “17”, “18” in table 6the casting machine operates in the second operating configuration (FIG.10) in which the machine is configured and structured to castsimultaneously two products in two moulds (14′, 14″) under the stirringaction of the molten bath by means of four linear stirrers or stirrerdevices (1′, 1″, 1′″, 1″″). In particular, a first stirrer device (1′)and a second stirrer device (1″) are arranged facing each other onopposite sides of the first mould (14′) and wherein a third stirrerdevice (1′″) and a fourth stirrer device (1″″) are arranged facing eachother on opposite sides of the second mould (14″). In this case both thefirst mould (14′) related to a first casting line and the second mould(14″) related to a second casting line are operative.

In the operating configuration indicated by “16”, on the first mould(14′), the first stirrer device (1′) and the second stirrer device (1″)exert both a force that is oriented downwards. On the second mould(14″), the third stirrer device (1′″) and the fourth stirrer device(1″″) exert both a force that is oriented downwards.

In the operating configuration indicated by “17”, on the first mould(14′), the first stirrer device (1′) and the second stirrer device (1″)exert both a force that is oriented upwards. On the second mould (14″),the third stirrer device (1′″) and the fourth stirrer device (1″″) exertboth a force that is oriented downwards.

In the operating configuration indicated by “18”, on the first mould(14′), the first stirrer device (1′) and the second stirrer device (1″)exert both a force that is oriented downwards. On the second mould(14″), the third stirrer device (1′″) and the fourth stirrer device(1″″) exert both a force that is oriented upwards.

It will be evident that table 1, table 2, table 3, table 4, table 5,table 6, have exemplary purposes only and that other combinations arealso possible on the basis of what has been previously described.

To conclude, the present invention relates to a control method of atleast three electromagnetic stirrer devices (1′, 1″, 1′″, 1″″) of thelinear type acting on metallic material in the molten state containedinside (FIG. 1, FIG. 9, FIG. 10, FIG. 11, FIG. 12) at least onesolidification mould (14, 14′, 14″) or contained inside a solidifiedmetallic shell of at least one metal rod (16) whose solidification is inprocess, wherein the metal rod (16) is produced by means of casting inthe at least one mould (14, 14′, 14″). The stirrer devices (1′, 1″, 1′″,1″″) are placed essentially at a same distance with respect to eachother according to a radial arrangement around the metallic material inthe molten state. Each of the stirrer devices (1′, 1″, 1′″, 1″″) isprovided with at least two induction coils (20′, 20″, 20′″) made ofwindings, the coils (20′, 20″, 20′″) of each of the stirrer devices (1′,1″, 1′″, 1″″) being placed (FIG. 9, FIG. 10) in line one after the otheralong a longitudinal development axis (23) of the electromagneticstirrer device according to a configuration in which the windings of thecoils (20′, 20″, 20′″) are essentially arranged on one single plane (24)which is parallel to the longitudinal development axis (23) of therespective stirrer device, the coil (20′, 20″, 20′″) being configuredand structured in such a way as to generate an electromagnetic field ofapplication of a stirring force on the metallic material in the moltenstate. The control method comprises at least one phase of switchingbetween two operating configurations of the electromagnetic stirrerdevices (1′, 1″, 1′″, 1″″). A first operating configuration is such thatat least one of the coils (20′, 20″, 20′″) of a first stirrer device(1′) of the stirrer devices (1′, 1″, 1′″, 1″″) is controlled in acoordinated way with corresponding other coils (20′, 20″, 20′″) of theother stirrer devices (1″, 1′″, 1″″) in such a way that the reciprocallycoordinated coils (20′, 20″, 20′″) generate a rotating electromagneticfield inducing in the metallic material in the molten state a rotationalmotion on a rotational plane which is essentially orthogonal withrespect to a direction of extraction (22) of the metal rod (16) from themould (14, 14′, 14″). A second operating configuration is such that atleast two of the coils (20′, 20″, 20′″) of the stirrer devices (1′, 1″,1′″, 1″″) are controlled in a reciprocally coordinated way with respectto each other in such a way that the reciprocally coordinated coils(20′, 20″, 20′″) generate a linear electromagnetic field inducing in themetallic material in the molten state a linear motion according to adirection parallel to the longitudinal development axis (23) of therespective stirrer device.

The first operating configuration is obtained by means of a series ofsub-phases of driving of the reciprocally coordinated coils (20′, 20″,20′″) in which each sub-phase of driving is a phase of supply of one ofsaid reciprocally coordinated coils (20′, 20″, 20′″) by means of adriving current supplied by a respective inverter (2′, 2″, 2′″, 2″″)between a driving branch of the respective coil (20′, 20″, 20′″) and acompensation branch of the inverter which is connected to a common starpoint of the coils (20′, 20″, 20′″) of the same stirrer device (1′, 1″,1′″, 1″″). The combination of the sub-phases of driving of thereciprocally coordinated coils (20′, 20″, 20′″) is such that the drivingcurrent supplied in a first sub-phase to one of the reciprocallycoordinated coils (20′, 20″, 20′″) is phase-shifted with respect to thedriving current supplied in a second sub-phase, which is subsequent tothe first sub-phase, to another one of the reciprocally coordinatedcoils (20′, 20″, 20′″).

In the case (FIG. 9) of four stirrer devices (1′, 1″, 1′″, 1″″) of thelinear type placed according to an opposite pairs configuration, thecombination of the sub-phases of driving of the reciprocally coordinatedcoils (20′, 20″, 20′″) is such (Table 1, operating configuration “0”)that the driving current supplied in the second sub-phase to one of thecoils (20′, 20″, 20′″) of the third stirrer device (1′″) isphase-shifted by 90° with respect to the driving current supplied in thefirst sub-phase to one of the coils (20′, 20″, 20′″) of the firststirrer device (1′), the driving current supplied in a third sub-phaseto one of the coils (20′, 20″, 20′″) of the second stirrer device (1″)is phase-shifted by 180° with respect to the driving current supplied inthe first sub-phase to one of the coils (20′, 20″, 20′″) of the firststirrer device (1′), the driving current supplied in a fourth sub-phaseto one of the coils (20′, 20″, 20′″) of the fourth stirrer device (1″″)is phase-shifted by 270° with respect to the driving current supplied inthe first sub-phase to one of the coils (20′, 20″, 20′″) of the firststirrer device (1′). In the case (FIG. 9) of four stirrer devices (1′,1″, 1′″, 1″″) of the linear type placed according to an opposite pairsconfiguration, the second operating configuration is obtained by meansof a series of sub-steps of driving of the coils (20′, 20″, 20′″) whichare configured and structured in such a way that the coils (20′, 20″,20′″) of at least one of the pairs of stirrer devices are controlled ina reciprocally coordinated way to operate according to an operating modeselected from various modes. In a first operating mode both stirrerdevices of the pair exert on the molten metal a force that isessentially oriented upwards (Examples: Table 1—operating configuration“1”, Table 2—operating configurations “3” and “4”, Table 3—operatingconfiguration “7”). In a second operating mode both stirrer devices ofsaid pair exert on the molten metal a force that is essentially orienteddownwards (Examples: Table 4—operating configuration “11”, Table5—operating configurations “14” and “15”, Table 6—operatingconfiguration “16”). In a third operating mode one of the stirrerdevices of said pair exerts on the molten metal a force that isessentially oriented upwards and the other one of the stirrer devices ofsaid pair exerts on the molten metal a force that is essentiallyoriented downwards (Examples: Table 1—operating configuration “2”, Table2—operating configurations “5” and “6”, Table 3—operating configuration“8”). In a fourth operating mode one alternates first time periods inwhich the stirrer devices of said pair operate in accordance with one ofa first operating mode, second operating mode, third operating modeform, and second time periods in which the stirrer devices of said pairoperate in accordance with an operating mode which is different fromthat of the first time period and is selected from first operating mode,second operating mode, third operating mode.

The terms upwards and downwards refer to the direction of the force ofgravity when the mould (14, 14′, 14″) is installed in an essentiallyvertical condition.

In the preferred solution of the present invention (FIG. 9, FIG. 10)each of the stirrer devices (1′, 1″, 1′″, 1″″) comprises three coils(20′, 20″, 20′″) of which a first coil (20′) which is placed upwards, asecond coil (20″) which is placed in an intermediate position withrespect to the first coil (20′) and to a third coil (20″) which isplaced downwards, the terms upwards and downwards referring to thedirection of the force of gravity when the mould (14, 14′, 14″) isinstalled in an essentially vertical condition. In this case the firstoperating configuration is obtained by means of a coordinated control of

-   -   at least the first coils (20′) of the stirrer devices (1′, 1″,        1′″, 1″″), generating a rotating electromagnetic field inducing        in the metallic material in the molten state a rotational motion        in correspondence of a higher position with respect to a body        (28) of the stirrer devices (1′, 1″, 1′″, 1″″);

or

-   -   at least the second coils (20″) of the stirrer devices (1′, 1″,        1′″, 1″″), generating a rotating electromagnetic field inducing        in the metallic material in the molten state a rotational motion        in correspondence of an intermediate position with respect to a        body (28) of the stirrer devices (1′, 1″, 1′″, 1″″);

or

-   -   at least the third coils (20′″) of the stirrer devices (1′, 1″,        1′″, 1″″), generating a rotating electromagnetic field inducing        in the metallic material in the molten state a rotational motion        in correspondence of a lower position with respect to a body        (28) of the stirrer devices (1′, 1″, 1′″, 1″″);

or

-   -   alternate phases of coordinated control in which each of said        alternate phases of control is selected from a phase of control        of the first coils (20′) only with the second coils (20″) and        the thirds coils (20′″) off, a phase of control of the second        coils (20″) only with the first coils (20′) and the third coils        (20′″) off, a phase of control of the third coils (20′″) only        with the second coils (20″) and the first coils (20′) off.

In the solution in which each of the stirrer devices (1′, 1″, 1′″, 1″″)comprises three coils (20′, 20″, 20′″), the second operatingconfiguration is obtained by means of a series of three sub-steps ofdriving of the coils, of which a first sub-step, a second sub-stepsubsequent to the previous one and a third sub-step subsequent to theprevious one, the second operating configuration being such that atleast the coils of one of said pairs of stirrer devices are controlledin a reciprocally coordinated way to operate according to an operatingmode selected from various modes. In the first operating mode bothstirrer devices of the pair exert on the molten metal a force that isessentially oriented upwards, said first operating mode being obtainedby providing in the first sub-step the driving current to the first coil(20′) of both stirrer devices of the pair, providing in the secondsub-step to the second coil (20″) of both stirrer devices of the pair adriving current which is phase-shifted by 120° with respect to thedriving current supplied in the first sub-step, providing in the thirdsub-step to the third coil (20′″) of both stirrer devices of the pair adriving current which is phase-shifted by 240° with respect to thedriving current supplied in the first sub-step. In the second operatingmode both stirrer devices of the pair exert on the molten metal a forcethat is essentially oriented downwards, said second operating mode beingobtained by providing in the third sub-step the driving current to thethird coil (20′″) of both stirrer devices of the pair, providing in thesecond sub-step to the second coil (20″) of both stirrer devices of thepair a driving current which is phase-shifted by 120° with respect tothe driving current supplied in the third sub-step, providing in thefirst sub-step to the first coil (20′) of both stirrer devices of thepair a driving current which is phase-shifted by 240° with respect tothe driving current supplied in the third sub-step. In the thirdoperating mode one of the stirrer devices of the pair exerts on themolten metal a force that is essentially oriented upwards and the otherone of the stirrer devices of said pair exerts on the molten metal aforce that is essentially oriented downwards, said third operating modebeing obtained by controlling the stirrer device of the pair whichexerts on the molten metal a force that is essentially oriented upwardsin such a way that in the first sub-step the driving current is suppliedto the first coil (20′), in the second sub-step a driving current issupplied to the second coil (20″) which is phase-shifted by 120° withrespect to the driving current supplied in the first sub-step, in thethird sub-step a driving current is supplied to the third coil (20′″)which is phase-shifted by 240° with respect to the driving currentsupplied in the first sub-step, said third operating mode being furtherobtained by controlling the stirrer device of the pair which exerts onthe molten metal a force that is essentially oriented downwards in sucha way that in the third sub-step the driving current is supplied to thethird coil (20′″), in the second sub-step a driving current is suppliedto the second coil (20″) which is phase-shifted by 120° with respect tothe driving current supplied in the third sub-step, in the firstsub-step a driving current is supplied to the first coil (20′) which isphase-shifted by 240° with respect to the driving current supplied inthe third sub-step.

The present invention also relates to a (FIG. 1, FIG. 13, FIG. 14, FIG.15) casting machine (18) provided with at least one solidification mould(14, 14′, 14″) of metallic material in the molten state and providedwith electromagnetic stirrer devices (1′, 1″, 1′″, 1″″) of the lineartype acting on metallic material in the molten state contained insidesaid at least one solidification mould (14, 14′, 14″) or containedinside a solidified metallic shell of at least one metal rod (16) whosesolidification is in process, wherein the metal rod (16) is produced bymeans of casting in the at least one mould (14, 14′, 14″), wherein thestirrer devices (1′, 1″, 1′″, 1″″) are placed essentially at a samedistance with respect to each other according to a radial arrangementaround the metallic material in the molten state, each of the stirrerdevices (1′, 1″, 1′″, 1″″) is provided with at least two induction coils(20′, 20″, 20′″) made of windings, the coils (20′, 20″, 20′″) of each ofthe stirrer devices (1′, 1″, 1′″, 1″″) being arranged in line one afterthe other along a longitudinal development axis (23) of theelectromagnetic stirrer device according to a configuration in which thewindings of the coils (20′, 20″, 20′″) are essentially arranged (FIG. 9,FIG. 10) on one single plane (24) which is parallel to the longitudinaldevelopment axis (23) of the respective stirrer device, the coils (20′,20″, 20′″) being configured and structured in such a way as to generatean electromagnetic field of application of a stirring force on themetallic material in the molten state. The casting machine (18) isprovided with a control unit (21) which controls at least the stirrerdevices (1′, 1″, 1′″, 1″″), the control unit (21) being configured andstructured to control the electromagnetic stirrer devices according to acontrol method in accordance with what has been previously described.

In one embodiment the casting machine (18) is provided with four stirrerdevices (1′, 1″, 1′″, 1″″) of the linear type, the casting machine (18)being configurable according to two operating configurations. In a firstoperating configuration the casting machine (18) is configured andstructured for the casting of the metal rod (16) which is one singlemetal rod (16) cast in one single mould (14) of the casting machine (18)under the stirring action of the molten bath by means of four stirrerdevices (1′, 1″, 1′″, 1″″) comprising a first stirrer device (1′), asecond stirrer device (1″), a third stirrer device (1′″), a fourthstirrer device (1″″), wherein the stirrer devices are placed accordingto an opposite pairs configuration, wherein the stirrer devices (1′, 1″,1′″, 1″″) are essentially placed at a same distance with respect to eachother and according to a radial arrangement along reciprocallyorthogonal axes around the metallic material in the molten state, afirst pair of stirrer devices (1′, 1″) consisting of the first stirrerdevice (1′) which is placed in a reciprocally faced condition withrespect to the second stirrer device (1″) along a first one of saidorthogonal axes according to an arrangement in which the metallicmaterial in the molten state is placed between the first stirrer device(1′) and the second stirrer device (1″), a second pair of stirrerdevices (1′″, 1″″) consisting of the third stirrer device (1′″) which isplaced in a reciprocally faced condition with respect to the fourthstirrer device (1″″) along a second one of said orthogonal axesaccording to an arrangement in which the metallic material in the moltenstate is placed between the third stirrer device (1′″) and the fourthstirrer device (1″″). In a second operating configuration the castingmachine is configured and structured for the simultaneous casting of twometal rods (16) in two moulds (14′, 14″) under the stirring action ofthe molten bath by means of four linear stirrers (1′, 1″, 1′″, 1″″), thecasting machine being provided with a first mould (14′) and with asecond mould (14″), the first mould (14′) being subjected to the actionof one pair of the linear stirrers (1′, 1″) comprising the first stirrerdevice (1′), the second stirrer device (1″), the second mould (14″)being subjected to the action of another pair of linear stirrers (1′″,1″″) comprising the third stirrer device (1′″), the fourth stirrerdevice (1″″).

The stirrer devices (1′, 1″, 1′″, 1″″) can be mounted inside the mould(14, 14′, 14″) or can be (FIG. 13, FIG. 14, FIG. 15) external and mobilein accordance with patent WO 2013/174512 in the name of the sameapplicant, to be considered as incorporated for reference. In this casethe casting machine is provided with stirrer devices (1′, 1″, 1′″, 1″″)which are associated with movement means (7, 8) along a development inlength of the metallic material rod (16). The movement means (7, 8)comprise coupling means (8) for the coupling with guiding means (7). Themovement means (7, 8) are intended for the movement of the stirrerdevices (1′, 1″, 1′″, 1″″) along the guiding means (7) at least for aportion of the total development in length of the metallic material rod(16) in different operating positions along the metallic material rod(16) which is a partially solidified metallic material rod (16) whichmoves within the cooling chamber (30). The metallic material rod (16) isnot completely solidified and consists of a shell in the solid statewhich encloses a core in the molten state which is intended to besubjected to the action of the electromagnetic field of application ofthe stirring force. For example (FIG. 15), the movement system cancomprise a motor (25) acting on a traction means (31) of a frame (34)which supports the stirrer. The traction means (31) for example canconsist of a cable or an equivalent means, which is made to pass in aseries of pulleys (29) and to which a counterweight (35) is fixed inorder to reduce the effort of the motor. The connection of theelectrical appliances of the electromagnetic stirrer device (1)preferably occurs by means of a connection box (9) placed in a protectedposition and preferably near the intermediate position with respect tothe complete stroke of the electromagnetic stirrer device (1) along theguide (7). The connection can occur by means of one or more flexibleelectrical cables (32) in such a way as to provide freedom of movementof the electromagnetic stirrer device (1) along the guide (7),optionally by means of the passage in a cable drag chain (not shown).The connection of the hydraulic appliances can occur in a completelysimilar way by means of one or more hoses for fluids (33) for feeding acooling fluid of the induction coils (12) to dissipate the heat comingfrom the rod (16).

Furthermore, the present invention also relates to a production plant ofmetallic material rods (16) comprising a casting machine (18) providedwith at least one solidification mould (14, 14′, 14″) of metallicmaterial in the molten state and provided with electromagnetic stirrerdevices (1′, 1″, 1′″, 1″″) of the linear type acting on metallicmaterial in the molten state contained inside said at least onesolidification mould (14, 14′, 14″) or contained inside a solidifiedmetallic shell of at least one metal rod (16) whose solidification is inprocess, wherein the metal rod (16) is produced by means of casting inthe at least one mould (14, 14′, 14″).

Furthermore, the present invention also relates to a casting process forthe production of metallic material rods (16) comprising a casting phasein which the metallic material is cast within at least one mould (14,14′, 14″) of a casting machine (18) for the extraction of the metallicmaterial rod (16) from the at least one mould (14, 14′, 14″). Themetallic material rod (16) coming out of the at least one mould (14,14′, 14″) is partially solidified and moves within a cooling chamber(30) of the casting machine (18), the metallic material rod (16)consisting of a shell in the solid state enclosing a core in the moltenstate. The casting process provides one or more stirring phases of thematerial in the molten state constituting the core and the stirringphase of the material in the molten state occurs according to a controlmethod of at least three electromagnetic stirrer devices (1′, 1″, 1′″,1″″) of the linear type acting on the metallic material in the moltenstate according to what has been previously described.

The description of the present invention has been made with reference tothe enclosed figures in a preferred embodiment, but it is evident thatmany possible changes, modifications and variations will be immediatelyclear to those skilled in the art in the light of the previousdescription. Thus, it must be underlined that the invention is notlimited to the previous description, but it includes all the changes,modifications and variations in accordance with the appended claims.

NOMENCLATURE USED

With reference to the identification numbers in the enclosed figures,the following nomenclature has been used:

-   1. Stirrer device-   1′. First stirrer device-   1″. Second stirrer device-   1′″. Third stirrer device-   1″″. Fourth stirrer device-   2. Inverter-   2′. First inverter-   2″. Second inverter-   2′″. Third inverter-   2″″. Fourth inverter-   3. Power supply input-   4. Reference input-   5. Control device-   6. Control stage-   7. Guiding means-   8. Coupling means-   (7, 8). Movement means-   9. Connection box-   9′. First connection box-   9″. Second connection box-   9′″. Third connection box-   9″″. Fourth connection box-   10. Distribution panel-   11 a. Stirrer device of the rotary type-   11 b. Stirrer device of the linear type-   12. Transformer-   13. Contactor-   14. Mould-   14′ First mould-   14″ Second mould-   15. Meniscus-   16. Metal rod-   17. Disconnector-   18. Casting machine-   19. Tundish-   20′. First coil-   20″. Second coil-   20′″. Third coil-   21. Control unit-   22. Direction of extraction-   23. Longitudinal development axis-   24. Plane-   25. Motor-   26. Power stage-   27. Current sensor-   28. Body-   29. Pulley-   30. Cooling chamber-   31. Traction means-   32. Electrical cable-   33. Hose for fluids-   34. Frame-   35. Counterweight

The invention claimed is:
 1. A method of controlling at least threeelectromagnetic stirrer devices, the at least three electromagneticstirrer devices being linear and acting on molten metallic materialcontained within at least one solidification mold so as to produce ametal rod, the at least three electromagnetic stirrer devices beingpositioned at equal distances from each other, each of the at leastthree electromagnetic stirrer devices having at least two inductioncoils, the at least two induction coils generating an electromagneticfield so as to create a stirring action in the molten metallic material,the method comprising: switching between a pair of operatingconfigurations of a rotary stirrer and a linear stirrer, a firstoperating condition of the pair of operating configurations controllingat least one of the at least two induction coils of one of the at leastthree electromagnetic stirrer devices in coordination with the at leasttwo induction coils of another of the at least three electromagneticstirrer devices so as to generate a rotating electromagnetic field so asto induce the molten metallic material to rotate in a rotational planeorthogonal to a direction of extraction of the metal rod from the atleast one solidification mold, a second operating condition of the pairof operating configurations controlling at least two of the at least twoinduction coils of the at least three electromagnetic stirrer devices ina reciprocally coordinated manner with respect to each other so as togenerate a linear electromagnetic field so as to cause linear motion ofthe molten metallic material in a direction parallel to a longitudinalaxis of the at least three electromagnetic stirrer devices, the firstoperating condition comprising: driving a series of sub-phases in the atleast two induction coils with a driving current supplied by an inverterbetween a driving branch of the respective at least two induction coilsand a compensation branch of the inverter, the compensation branch beingconnected to a common star point of the at least two induction coils ofthe respective at least three electromagnetic stirrer devices, thedriving current supplied to a first sub-phase of the series ofsub-phases being phase-shifted with respect to the driving currentsupplied to another of the at least two induction coils in a secondsub-phase of the series of sub-phases subsequent to the first sub-phase.2. The method of claim 1, wherein the at least three electromagneticstirrer devices comprise four electromagnetic stirrer devices arrangedin opposing pairs, a first pair of the four electromagnetic stirrerdevices having a first stirrer and a second stirrer in which the firststirrer faces the second stirrer, a second pair of the fourelectromagnetic stirrer devices having a third stirrer and a fourthstirrer facing each other along another orthogonal axis such that themolten metallic material is between the third stirrer and the fourthstirrer.
 3. The method of claim 2, the step of driving comprising:phase-shifting the driving current in the second sub-phase to one of theat least two induction coils of the third stirrer by 90° with respect tothe driving current supplied in the first sub-phase to one of the atleast two induction coils of the first stirrer; phase-shifting thedriving current in a third sub-phase to one of the at least twoinduction coils of the second stirrer by 180° with respect to thedriving current supplied to the first sub-phase to one of the at leasttwo induction coils of the first stirrer; and phase-shifting the drivingcurrent in a fourth sub-phase to one of the at least two induction coilsof the fourth stirrer by 270° with respect to the driving currentsupplied in the first sub-phase to one of the at least two inductioncoils of the first stirrer.
 4. The method of claim 2, the secondoperating condition comprising: exerting an upwardly oriented force onthe molten metallic material by the at least three electromagneticstirrer devices.
 5. The method of claim 2, the second operatingcondition comprising: exerting a downwardly oriented force on the moltenmetallic material by the at least three electromagnetic stirrer devices.6. The method of claim 2, the second operating condition comprising:exerting an upwardly oriented force on the molten metallic material byone of the at least three electromagnetic stirrer devices; and exertinga downwardly oriented force on the molten metallic material by anotherof the at least three electromagnetic stirrer devices.
 7. The method ofclaim 6, the second operating condition comprising: alternating timeperiods in which the at least three electromagnetic stirrer devicesexert the upwardly oriented force and the downwardly oriented force. 8.The method of claim 1, wherein each of the at least threeelectromagnetic stirrer devices has three induction coils in which afirst induction coil is positioned upwardly, a second induction coil isplaced in an intermediate position between the first coil and a thirdcoil, the third coil being placed in a downward position.
 9. The methodof claim 8, the first operating condition comprising: generating arotating electromagnetic field by the first induction coil of the atleast three electromagnetic stirrer devices.
 10. The method of claim 8,the first operating condition comprising: generating a rotatingelectromagnetic field by the second induction coil of the at least threeelectromagnetic stirrer devices.
 11. The method of claim 8, the firstoperating condition comprising: generating a rotating electromagneticfield by the third induction coil of the at least three electromagneticstirrer devices.
 12. The method of claim 8, the second operatingcondition comprising: driving current to the first induction coil toboth electromagnetic stirrer devices of a first pair so as to exert anupwardly oriented force to the molten metallic material; phase-shiftingthe driving current to the second induction coil of the first pair ofthe at least three electromagnetic stirrer device by 120° from step ofdriving current to the first induction coil; and phase-shifting thedriving current to the third induction coil of the first pair of the atleast three electromagnetic the stirrer device by 240° with respect tothe step of driving current to the first induction coil.
 13. The methodof claim 8, the second operating condition comprising: exerting adownwardly oriented force on the molten metallic material by a first ofelectromagnetic stirrer devices, the step of exerting comprising:driving current to the third induction coil of both of the first pair ofthe at least three electromagnetic stirrer devices; phase-shifting thedriving current to the second induction coil of both of the first pairof the at least three electromagnetic stirrer devices by 120° withrespect to the driving current of the third induction coil; andphase-shifting the driving current the first induction coil of the firstpair of the at least three electromagnetic stirrer devices by 240° withrespect to the driving current to the third induction coil.
 14. Themethod of claim 8, the second operating condition comprising: exertingan upwardly oriented force on the molten metallic material by oneelectromagnetic stirrer devices of a first pair; and exerting adownwardly oriented force on the molten metallic material by anotherelectromagnetic stirrer device of the first pair.